The accuracy of the phase fraction determined by time-of-flight neutrondiffraction measurement at iMATERIA was verified by preparing model samplesconsisting of laminations of ferritic and austenitic stainless-steel sheets.Rietveld texture analysis, based on 132 diffractograms, was employed as theanalysis method. The analyzed volume fractions of austenite agree with theprepared fractions (0.61–49.3 vol%) with a maximum error of only 5%, relativeto the prepared fractions. This is due to the excellent fitting quality of the multidiffractogram-based Rietveld refinement with consideration given to the texturesof both the major and minor phases. Although the quality of the textureanalysis for the austenite phase becomes poor, at\5 vol%, the consideration ofthe textures improves the accuracy of the phase fraction determination. Alsodescribed is how the textures affect the phase fractions, as determined by theconventional diffraction method. It is clearly shown that texture cannot beignored in phase fraction analysis and, in turn, a reasonable consideration of thetexture realizes precision in the analysis.

The authors have developed the texture measurement system at iMATERIA, which is the neutron diffractometers built in Materials and Life Science Experimental Facility (MLF) at J-PARC, Japan. The high flux of the incident beam and Time-Of-Flight method enabled the complete texture measurement within several minutes in case of steels. Since the neutron beam can transmit most of the materials, the measured texture represents the state of whole exposed volume. The multi-histogram analysis also enables to determine phase fractions in a multiphase material as well as the texture of each phase.

A rapid texture measurement system has been developed on the time-of-flight neutron diffractometer iMATERIA (beamline BL20, MLF/J-PARC, Japan). Quantitative Rietveld texture analysis with a neutron beam exposure of several minutes without sample rotation was investigated using a duplex stainless steel, and the minimum number of diffraction spectra required for the analysis was determined experimentally. The rapid measurement scheme employs 132 spectra, and by this scheme the quantitative determination of volume fractions of texture components in ferrite and austenite cubic phases in a duplex stainless steel can be made in a short time. This quantitative and rapid measurement scheme is based on the salient features of iMATERIA as a powder diffractometer, i.e. a fairly high resolution in d spacing and numerous detectors covering a wide range of scattering angle.

Texture is an important property especially for metallic materials having hexagonal close-packed crystal structure. In order to understand the overall property or change in the microstructure of materials, neutron diffraction is a powerful tool of investigation. In this study, we attempt to measure the textures of Ti–6Al–4V (mass%) alloy by using a time-of-flight neutron diffractometer, iMATERIA. The results indicate that the texture measurement for the hexagonal phase is possible with the same method as for cubic metals. The texture of cubic beta phase, whose volume fraction is several percent, can simultaneously be determined together with the hexagonal alpha phase.

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研究論文（学術雑誌）

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Improvement of Magnetostrictive Properties of Fe-15mol%Ga Alloy by Texture Formation during High Temperature Uniaxial Compression Deformation

The texture control of Fe–Ga solid solution alloy is examined by high temperature deformation, based on the previously suggested mechanism of high temperature deformation texture formation, “preferential dynamic grain growth (PDGG)”. As the result of uniaxial compression deformation of Fe-15 mol% Ga alloy at 1173 K, sharp alignment of <001> along the compression axis was observed. Microstructural observation by EBSD revealed that the <001> alignment was attributable to the growth of <001> oriented grains. The observed textures and microstructures were similar to those seen in the previous studies of Fe–Si alloys, in which the activation of PDGG was confirmed. Based on these facts, it is concluded that PDGG can be applied as a texture control technique for Fe–Ga alloy. The deformed sample showed larger saturation magnetostriction than the sample without deformation, indicating the effectiveness of the texture control by high temperature deformation.

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研究論文（学術雑誌）

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圧延鋼板に対する中性子回折ラインプロファイル解析における散乱ベクトル方位の影響

塙健太，小貫祐介，轟秀和，齋藤洋一，鈴木茂，佐藤成男

Ｘ線分析の進歩

アグネ技術センター

48, 338-345

2017/03/31

We investigated the effect of the relationship between the scattering vector of neutron diffraction and the sample direction processed by cold-rolling on line-profile analysis. It was revealed that dislocation parameters became unstable when using a diffraction profile at the scattering vector parallel to the rolling direction. This is probably due to the inhomogeneous elastic strain caused by the distribution of the Poisson’s effect depending on the crystallographic orientation. On the other hand, the most ideal direction of the scattering vector for the line profile analysis is the normal direction of the rolled sheets. This is because the inhomogeneous elasticstrain and the residual strain was small in this direction. The contribution of austenite and ferrite phases in the duplex stainless steels to the work hardening was also investigated by estimating dislocation density. The dislocation density in the austenite phase was much higher than that in the ferrite phase. Consequently, the austenite phase is mainly responsible for the work hardening with the cold-rolling.

The authors measured texture change during uniaxial tensile deformation of extruded bar of AZ31 magnesium alloy by time-of-flight neutron diffraction and EBSD (electron backscatter diffraction). Texture measurement by neutron diffraction revealed the transition of tensile axis distribution in overall gauge volume during the deformation. The concentration of the tensile axis initially observed at 〈213̄0〉. With increasing strain, the dominant peak appeared at 〈9 1 ̄10 0〉 and the initial peak weakened. It was also found that the total density of 〈hki0〉 decreased during the deformation. EBSD showed activations of {101̄1} compression twinning and following double twinning. The twinned region were oriented away from the 〈hki0〉 orientation group. The amount of twinning gradually increased with increasing strain. On the other hand, the deformation of the matrix was achieved by slip deformation, resulting in the formation of the peak at 〈9 1 ̄10 0〉. Based on the above results, it was concluded that the reason for poor ductility of magnesium alloys may not be a lack of 〈c+a〉 slip but twinning and deformation concentration inside of the twins.

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Local stress development in polycrystalline Fe-17mol%Ga alloy under tensile loading e In situ measurement using synchrotron X-ray micro-beam

&nbsp;&nbsp;We have performed high-sensitivity magnetic measurements for tensile-deformed SUS304-type austenitic stainless steel to elucidate a relationship between morphology of martensite particles and structure-sensitive magnetic hysteresis properties. A monotonic increase of the volume fraction of martensite phase up to 14.3% through strain-induced martensitic transformation was observed, while coercivity exhibits a maximum at around 4.3% fraction. Measurements of coercivity varying the magnetic-field direction against tensile direction revealed anisotropy in angular dependence of coercivity that becomes weaker with the progress of plastic deformation. These observations were explained as due to a change of the size and anisotropy in shape of martensite phase with deformation.<br>

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研究論文（学術雑誌）

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High-Speed Rolling of AZ31 Magnesium Alloy Having Different Initial Textures